Send a Copy of Non-Delivery Report to
If a message is undeliverable, it is returned to the sender with a non-delivery report (NDR). You can designate that copies of the message and the NDR are sent to a specific mailbox. For example, you can designate that all NDR copies go to Postmaster@your domain.

To assign a designated mailbox to receive copies of all NDRs, type an e-mail address in the Send a Copy of Non-Delivery Report to box.